Numerous closures for container bodies, such as metallic cans, glass or plastic bottles or jars and the like are known. For bottles or jars, resealable closures, in the form of metallic screw-on caps or tops, are commonplace. For metallic cans that contain beverages, such as beer and soft drinks, however, no commercially successful resealable closure is known. The commercially employed closure elements for can bodies include the ring-pull or "pop top" can end and the nondetachable or "stay-on-tab" can end.
In the case of metallic cans, the inability to provide a practical resealable closure device has limited, at least in the case of beverage cans, the size of the container. Thus, while plastic and glass bottles having a capacity as high as two liters have become commercially successful, metallic beverage cans have been limited, for the most part, to single serving sizes, having a maximum capacity of about 16 ounces (0.473 liters). It is thus a primary objective of the present invention to provide a resealable closure device for metallic can bodies which will enable metallic cans to serve the large capacity beverage container market.
It is also a primary objective of the present invention to provide a resealable closure device which may be employed on metallic cans whether the contents of the container are packaged under a vacuum, are at atmospheric pressure or are internally pressurized.
It is another primary object of the present invention to produce a resealable closure device which can be seamed to a can body according to the methods and using the equipment commonly found in the can filling lines. Thus, it is an objective of the present invention to provide a resealable closure which, in part, comprises a metallic end.
It is an additional objective of the present invention to employ an "over-center" sealing mechanism. In such a sealing mechanism, a flexible closure element is molded in an upstanding or "inverted umbrella" position. When in place, the closure element is inverted on itself, causing the element to tighten itself in place.
The use of the over-center sealing mechanism has been described in the literature. However, none of the known over-center closure devices have been successfully commercially applied to a metallic can used for such purposes as for containing beverages and the like.
U.K. patent application No. GB2091706A illustrates, in one embodiment, an over-center closure device for a container having an external bead about its mouth. The closure device is in the form of a flexible element having a skirt portion which can be moved with respect to the plane surface of the closure device from an upwardly extending position to a downwardly extending position where a bead formed on an internal surface of a connecting portion between the plane surface and the connecting device and the skirt or lever portion engages a sloping surface of the container mouth bead. In the lowered position, the skirt or releasing flange extends at an angle away from the container wall and makes no contact therewith. Also, with the skirt extending upwardly, the closure element cannot be snugly seated on the container wall.
An immediate problem with the closure device of this reference is apparent from the fact that the skirt extends outwardly from the container wall thus leaving the sealing connection between the closure device's bead and the bead of the container mouth exposed to dirt and other debris which may be encountered in using the container. The exposed location of the skirt also allows for accidental premature opening of the container during shipping and storage and does not permit close packing of the containers. In addition, in the event the contents of the container are pressurized, it appears that the portion of the closure device's bead in contact with the mouth bead would be insufficient to prevent blow off of the closure device particularly where elevated pressures are encountered in the container. One reason for this is that the slope of the surface of the mouth bead is insufficient. Another reason is that the upward bulging of the top of the closure tends to rotate the skirt further downwardly about the mouth bead, and since the skirt is not restrained from such movement, a leveraged pressure is placed on the relatively small area of the closure device bead in contact with the mouth bead, creating a tendency for the closure device bead to deform. Further, it would be difficult to control venting of the contents of the container with such a closure device in the event the contents were pressurized.
French published patent application No. 2,377,333 illustrates an over-center device for glass bottles. In this device, an over-center tightening element is attached to an end wall portion of the closure. When in its closed position, the tightening element pulls the end wall against the mouth of the bottle, with sealing occurring only at the top surface of the bottle.
Problems with this closure come from the location of the seal. Internal pressure acting against the end wall of the closure may lift the end wall from the mouth of the bottle, possibly causing leakage of pressure and/or the product from the container. Additionally, with sealing on the end of the bottle mouth alone, no provision is made for controlled venting of internal pressure when opening the bottle using this closure device. Thus, when returned to its loosened position, internal pressure within the bottle will tend to blow the closure off of the bottle uncontrollably, a result which is unacceptably dangerous for the consumer.
Another known over-center closure device is described in U.S. Pat. No. 4,376,493. In this patent, a large diameter can, such as a paint can, includes a cover which locks onto the can. There are also problems involved with this closure which make it unacceptable for pressurized cans.
This patent requires that the can body have a downwardly directed flange and that the closure device hook under the lip of the flange. This has been found to be unacceptable for several reasons. The resilient materials, such as plastics resins, forming such closure devices tend, over time, to permanently deform or "creep" somewhat. This deformation makes it difficult to remove the closure of this patent from the can and may cause damage to the flange of the can or the sealing surface of the closure during removal. This deformation, with or without the additional problem of flange damage, also makes resealing of the container difficult.
Another problem with the structure of this patent lies in the region of sealing between the closure and the can. In this patent, it is preferred that sealing also occur between a well or wall of the closure and the inner side wall of the container. The seal continues around the flange and may continue under it, unless spaced locking members are employed. Such a seal will not controllably vent internal pressure within the can when opened, again creating the possibility of allowing the internal pressure to blow the closure element off of the container when the closure is returned to the unlocked position.
An additional problem caused by the presence of a central plug member, especially in pressurized cans, is the tendency of the internal pressure to push against the plug, causing the plug to displace upwardly, resulting in additional stresses on the locking mechanism and possibly destroying the central seal.
Another known over-center closure device is shown in U.S. Pat. No. 4,387,820. This patent, similar to U.S. Pat. No. 4,376,493, relies upon contact between an inner wall of the container and the closure element for sealing, with the seal continuing against the mouth at the top of the container. A plurality of spaced locking means hook under the container bulge or groove to close the container. Such a closure cannot seal on the outer periphery of the container, due to the presence of the spaced locking levers. Further, the inner surface seal eliminates any change of controlled venting, again allowing occurrence of the blow off problem previously described.
It is thus a primary objective of the present invention to provide an over-center closure device which overcomes the shortcomings of the known devices of this type.